Jameson is an Illegal robo that appears in Custom Robo V2 and Custom Robo Arena. It is a primarily autonomous robo that is noted for its ENORMOUS size. It doesn't belong to any model "family", but it is most similar to a Lightning Sky robo in Arena.
Jameson is first encountered as the penultimate boss of the Custom Robo V2 story mode. It is used by Rokudou, the leader of Goliath as a last ditch effort to stop the hero from defeating Goliath. However, unlike other commanders, Rokudou doesn't dive into Jameson due to an illness he has. Jameson is eventually defeated by the hero. Jameson later appears in the Grand Battles when Goliath escapes and is fought for a second time at the Goliath Base.
Jameson later appears in Custom Robo Arena. It first appears in a dream sequence at the beginning of the game. It is impossible to defeat as the fight ends early.
Two Jamesons are encountered at the Encephalon Isle lab (Greybaum's secret base) as Gatekeeper Systems that prevent intruders from progressing further in. The hero eventually defeats both autonomous robos. Jameson later appears in the Underground during the Grudge Matches.